The recent rapid developments in semiconductor industry have resulted in accelerating the increase of input and output terminals, the increase of signal processing speed and power consumption, and the requirement of high-density packaging. According to the high-integration of a semiconductor, a large amount of leads were required and a gap between leads was decreased, thereby making the design and assembling of a semiconductor lead frame more difficult. Moreover, as the increase of signal processing speed and power consumption caused the increase of heat generation, a heat sink was installed on a semiconductor package additionally, or a package material having a good heat conductivity was used to reduce the heat. Further, the COB (Chip On Board) method for directly mounting a chip on a printed circuit board or stacked packaging method have been used to meet the requirement of high-density packaging.
FIG. 1 is a top view of a conventional semiconductor lead frame. The semiconductor lead frame includes a semiconductor chip 11, a tetragonal die pad 12 for mounting the semiconductor chip 11, tie bars 13 provided at four edges of the die pad 12 for supporting the die pad 12, lots of inner leads 14 uniformly formed with a predetermined distance from the die pad 12, wires (not shown) for connecting a bonding pad formed on the semiconductor chip 11 to the inner leads 14, outer leads (not shown) for connecting the inner leads 14 to outside parts, and tapes 17 attached on the inner leads 14 to prevent the deformation of the inner leads 14.
In the above described conventional semiconductor lead frame, when semiconductor chips of a different size are mounted on a same kind of semiconductor package and if a chip size is smaller than die pad size, there occurs a sweeping, that is, the phenomenon that the wires are clustered together at one side during the molding process, or the phenomenon that the wires stick together. On the other hand, if a chip size is larger than a die pad size, a new semiconductor lead frame with a die pad of a proper size should be prepared.
Moreover, in the conventional semiconductor lead frame, the distance between the semiconductor chip and the inner leads in edge size is longer than that in lateral side, thereby the length of wires becoming different from each other at the time of bonding process. This increases the wire consumption during the production of a semicondutor package, resulting in the increase of a production cost and shortening a lifetime of a wire bonding apparatus.